1. Field of the Invention
The present application generally relates to outboard motors, and more particularly to outboard motors with idle regulating valves for providing secondary air to an internal combustion engine of the outboard motor.
2. Description of the Related Art
Watercraft vehicles, such as boats, are often powered by an outboard motor having an internal combustion engine. The outboard motor may have an air intake system for controlling the amount of air delivered to the internal combustion engine. Japanese Patent Application HEI 2001-152895 discloses an outboard motor having a multi-cylinder internal combustion engine and an air intake manifold for delivering atmospheric air into the internal combustion engine. A throttle valve controls an opening of an intake passage in the air intake manifold thereby controlling the amount of primary air delivered into the engine's combustion chambers. An idle regulating system can supply secondary air to the engine via the intake passage to prevent stalling. The regulating system receives atmospheric air and then delivers the atmospheric air as secondary air through a bypass tube of the regulating system and into the intake passage of the air intake manifold.
A fuel injection system and the air intake manifold cooperate to control the air/fuel mixture delivered to combustion chambers. A throttle valve can be used to control the amount of air delivered to the internal combustion engine through the intake passage, and a fuel injection valve of the fuel injection system can control the amount of fuel supplied to the engine chambers. By controlling the amount of air and fuel delivered to the engine, a desired driving state (e.g., low engine speeds, high engine speeds, etc.) can be achieved.
When the watercraft is moving, the throttle valve of the outboard motor can be quickly closed in order to decelerate the watercraft. That is, the throttle valve can be closed to reduce the amount of secondary air delivered to the internal combustion engine, thereby reducing the engine speed and the outboard motor's power output. When the internal combustion engine speed is rapidly decelerated in this manner, the required amount of intake air to operate the engine is reduced. Nevertheless, conventional engines may deliver an insufficient amount of secondary air through the intake system to the internal combustion engine when the throttle valve is quickly closed and, thus, may result in stalling, for example.
When the throttle valve is quickly closed, a negative pressure in a surge tank of the engine may be significantly increased. Conventional engines may have a sensor to detect a negative pressure in the surge tank. When a relatively large, rapid increase of negative pressure is detected in the surge tank, the regulating valve can be opened to allow secondary air to flow into the surge tank to reduce the negative pressure. The secondary air is often delivered through the regulating valve, the bypass tube, and to the internal combustion engine. In this manner, when the throttle valve is rapidly closed, secondary air is delivered to the internal combustion engine to maintain operation of the engine. Thus, the secondary air delivered to the engine can prevent unintentional engine stalling. Unfortunately, conventional engines typically have regulating valves that undesirably increase the overall engine size. For example, conventional outboard motors may have idle regulating valves that are positioned above an internal combustion engine and an air intake manifold. Thus, the idle regulating valve increases the overall engine size. Additionally, a conventional outboard motor may have a complicated design with many parts, such as an idle regulating system comprising an idle regulating valve and an intake bypass tube, which provides communication between the intake passage in the air intake manifold and the idle regulating valve.